A BGA package is an IC package wherein the leads of a device (DUT) 50 are formed as solder ball terminal pins having the shape of a hemisphere. The number of terminal pins of the BGA package is 100-300 wherein a space between the adjacent pins is, for example, 1.27 mm or 1.0 mm.
An IC test system performs characteristics analysis or go/no-go tests of a DUT 50 through various types of electrical test. For doing the tests, the DUT 50 is mounted on an IC socket to undertake the electrical test and is removed from the IC socket after the tests. Such connection and disconnection between the DUT and the IC socket are performed frequently since a large number of DUTs 50 are tested by an IC test system. Hence, the contact between the DUT 50 and the IC socket gradually will become loose and cause contact problems, or the contact pressure will become too weak to cause a contact instability.
The structure of the contact area of a conventional IC socket used for testing a BGA package type device is explained in the following with reference to FIGS. 3 and 4.
The structure of test-head of the IC test system is composed of a device press mechanism 68 shown in FIG. 3, an IC socket, and a contact board 70 shown in FIG. 4.
The IC socket is composed of a socket housing 62 and a plurality of contact pins 64. The IC socket is mounted on the contact board 70. The DUT 50 is pressed downward against the IC socket by the device press mechanism 68 to establish an electric contact.
The contact pin 64 is a plate spring type pin. The upper terminal of this plate spring pin establishes an electric contact by the contact pressure applied against the hemisphere solder bump of the terminal pin of the DUT 51. In the lower terminal of the contact pin 64, an electric contact is established with a terminal pattern 72 on the surface of the contact board 70 by the contact pressure therebetween. The terminal pattern 72 may also be formed of through holes where the contact board 70 and the lower terminal of the contact pin 64 are connected by means of soldering to form an electric connection.
An overall shape of the contact pin 64 is a vertically arranged plate spring with a curve at its center to create the spring characteristic to maintain electric contact pressure for the lower and upper portions thereof.
This contact pin 64 is integrated to the socket housing 62. The contact pins are arranged in a lattice shape manner at positions which match the corresponding terminal pins 51 of the DUT. Each of the terminal pins 51 contacts with the corresponding terminal pattern 72 directly below the DUT to form an electric contact, thereby the electric connection is established from the lower portion of the contact board 70 to the device test system 80.
Alternatively, an electric contact is formed by a through holes and soldering at a position directly below each of the contact pins 64, thereby establishing an electric connection from the lower portion of the contact board 70 to the device test system 80.
Device press mechanism 68 secures the perfect contact between all of the contact pins 64 and the DUT mounted on the IC socket. The device press mechanism has a structure for downwardly pressing the DUT by, for example, a manual force or air pressure. This downward pressure is set to be considerably high so that all the hemisphere shape pins 51 of the device are securely connected to the contact pins. As a consequence, the spring force of the IC socket tends to be weakened. Thus, there arise contact defects or contact instabilities in the contact pin 64. Such IC sockets involving the contact problems must be immediately exchanged. In general, the contact pins are considered to be disposable since they must be exchanged after the predetermined number of use or the predetermined length of time.
As explained above, the connection and disconnection operations are repeated many times for the IC socket for electrically testing the DUT 50 by the IC test system. Thus, even when there is only one contact pin 64 which shows the defective contact performance or contact instability, the whole IC socket has to be replaced.
When the connection is made through the soldering, the solder has to be removed in order to replace the IC socket and soldering must be applied again for establishing the connection, which increases the time and cost of the replacement.
In addition, since the number of the terminal pins, alignment or pitch of the pins of DUT 50 vary in various ways, many IC sockets corresponding to the various conditions must be prepared accordingly. Thus, the IC sockets cannot be commonly used for varying devices.
Therefore, an object of the present invention is to provide an IC socket structure which can be used for various types of device test by having a structure in which the IC socket is divided in a block by block basis so that defective contact pins can be replaced as a contact block.